This invention relates to a braking apparatus and braking method for a vehicle, more specifically, to a technology for rapid braking.
As a braking force assist method, a brake system of a vehicle has often been provided with a booster for assisting a force of the driver to press down the brake pedal. The booster utilizes a negative pressure or the like, generated in the intake manifold of the engine, to operate a power piston having a constant area for assisting the braking force.
Further, as a braking force assist method for rapid braking in an emergency, one which varies the braking characteristics to a safety side, if the distance from another vehicle running in front is less than a predetermined value, or a relative speed is more than a predetermined value, has been disclosed, for example, in Japanese Patent Laid-open Publication 05-42862.
A known booster has been designed so that assist by a negative pressure is not started unless the brake pedal is operated by a predetermined pressing force, and the output (brake pressure) obtained through the booster is uniformly set relative to the force of pressing down the brake pedal. Therefore, for a driver who tends to be weak in providing a brake pedal operating force, the brake pressure does not immediately increase when the brake pedal is pressed down. Thus, a time period is required before braking action begins. In particular, when the vehicle is to be stopped in an emergency, it may be difficult to sufficiently utilize the brake performance.
The brake operation condition differs depending on various traffic environments such as vehicle travel on a city road, a mountain road, or a crowded road. The brake operation condition also differs depending on the operation tendency (driving condition) intended by the driver such as a driver desiring normal driving, sporty driving hard driving and the like.
Since the above conventional techniques do not consider traffic environments for the vehicle or driving tendency intended by the driver, a determination of rapid braking may be uncertain under different traffic environments or under different driving tendencies.